Add GitHub Actions, trim jobs from Travis

.github/workflows/unf_ext.yml

@@ -0,0 +1,49 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: >-
+      ${{ matrix.os }} ${{ matrix.ruby }}
+
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ ubuntu-20.04, macos-11.0, windows-2019 ]
+        ruby: [ 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, head ]
+        include:
+          - { os: windows-2019, ruby: mingw }
+        exclude:
+          - { os: macos-11.0  , ruby: 2.2   }
+          - { os: macos-11.0  , ruby: 2.3   }
+          - { os: windows-2019, ruby: head  }
+
+    steps:
+      - name: repo checkout
+        uses: actions/checkout@v2
+
+      - name: load ruby, ragel
+        uses: MSP-Greg/setup-ruby-pkgs@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          mingw: _upgrade_
+
+      - name:  bundle install
+        shell: pwsh
+        run:   |
+          # update RubyGems in Ruby 2.2, bundle install
+          if ('${{ matrix.ruby }}' -lt '2.3') {
+            gem update --system 2.7.10 --no-document
+          }
+          bundle config set --local path .bundle/vendor
+          bundle install --jobs 4 --retry 3
+
+      - name: compile
+        timeout-minutes: 5
+        run:  bundle exec rake compile
+
+      - name: test
+        timeout-minutes: 5
+        run:  bundle exec rake test

.travis.yml

@@ -6,16 +6,7 @@ rvm:
   - 1.9.3
   - 2.0
   - 2.1
-  - 2.2
-  - 2.3
-  - 2.4
-  - 2.5
-  - 2.6
-  - 2.7
-  - ruby-head
 matrix:
-  allow_failures:
-    - rvm: ruby-head
 before_install:
   - gem update --system --conservative || gem install --conservative bundler -v '<2'
 before_script: